Egyptian opposition parties have formed a coalition against proposed changes to the constitution that would allow President Abdel-Fattah al-Sisi to stay in office well beyond the end of his current term in 2022, two opposition leaders said on Wednesday.Egypt's parliament has given its preliminary approval to the changes, after two-thirds of the general committee endorsed the proposed amendments on Tuesday.The 596-seat assembly - which is packed with al-Sisi supporters - will take a final vote on February 17, but the amendments would also need to be put to a national referendum.Abdel-Aziz el-Husseini, a senior leader in the Karama, or Dignity party, said that 11 parties met the previous day and declared their opposition to the proposed changes. The group established a "union for the defence of the constitution" that includes secular and left-leaning parties and lawmakers, he added.Khaled Dawood, another opposition leader and former head of the liberal Dostour, or Constitution party, questioned the legitimacy of the process to amend the 2014 charter, citing a constitutional clause that bars extending the two-term limit."We will challenge the proposed amendment before the country's Supreme Constitutional court," he said.Amending the constitution was widely expected. Pro-government lawmakers and media figures have argued for years that the constitution is crippling the president's efforts to advance the country, including overhauling its economy and defeating Islamic militants. Al-Sisi himself said in 2015 that "the constitution was drafted with good intentions."A draft of the proposed amendments shows concerted efforts by the pro-government "Supporting Egypt" coalition to consolidate al-Sisi's power. The 64-year-old leader could be allowed to run for a third and fourth six-year term, potentially extending his rule to 2034.Talaat Khalil, a lawmaker attending Monday's meeting, decried the proposed changes, especially a broad clause stating the military's duty is to protect "the constitution and democracy and the fundamental makeup of the country and its civil nature."He told a press conference on Monday that this could allow the armed forces to support one politician at the cost of another. "And this is a great danger," he said.Experts say opposition parties are too weak to effectively challenge the amendments amid an unprecedented crackdown on dissent."Any move from the opposition will be met with harsh reactions," said Ahmed Abd Rabou, a visiting assistant professor at the University of Denver. "The only pragmatic option is to campaign for a 'NO' to the foreseeable amendments."Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.